Metamorphic evolution of south Indian granulites: New insights from in-situ U-Pb dating and Nd-Hf isotope fingerprinting of zircon, titanite, monazite, and apatite

Abstract

The Precambrian Southern Granulite Terrane (SGT) of south India is well known for the preservation of high to ultrahigh-temperature granulite facies metamorphic rocks, with their formation linked to the assembly of the East Gondwana supercontinent. Although the timing and duration of this Himalayan-scale collisional orogeny is well characterized, the peak to post-peak evolutionary history of these granulitic rocks is poorly understood. This study attempts to characterize the peak to post-peak metamorphic evolutionary history of south Indian granulites using in-situ accessory mineral geochronology and isotopic fingerprinting of a metapyroxenite sample collected from the central part of SGT. UPb dating of zircon and monazite from the sample constrains the timing of peak metamorphism at 560–550 Ma, while the timing of fluid activity and cooling was characterized using titanite (557 ± 2 Ma) and apatite (410 ± 3 Ma) dating. UPb ages recovered from available accessory phases, together with temperature estimates from trace element thermometry and closure temperature estimates, suggest variable and slow cooling rates for the studied granulite. On the other hand, HfNd isotopic fingerprinting of zircon and titanite points to the involvement of slab-derived materials during peak metamorphism, providing new evidence for melt/fluid-assisted metamorphism in the area.